For many years, oil from beneath the surface of a field has been pumped by means of a pumping unit which reciprocates a polished rod connected to a drill string to operate a submerged pump. Various types of pumping units are available such as those in Jennings (U.S. Pat. No. 990,743), Wacker (U.S. Pat. No. 1,269,343), Chapman et al. (U.S. Pat. No. 1,277,382) and Kammerer et al. (U.S. Pat. No. 1,655,062). In these patents various means are provided to ensure the true vertical movement of the polished rod. However, in all these devices, the movement of the polished rod is derived from cables or ropes. While these patents do provide means for pumping oil from beneath a surface, the operational characteristics were such that some improvements were desired.